Load limiting clutch



Nov. s, 1949 w. C.' STARKEY 2,487,280

LOAD LIMAITING CLUTCH i" BY Z5 Trax/V526,

ov. 8, g49 w- C. STARKEY 2,487,280

. LOAD LIMITING CLUTCH Filed DeC. 20, 1944 2 Sheets-Sheet 2 INVENTOR. /AL//sw 7i/Fara# SW7/fwn:

BY Ww .Patented N0 8 1.949

William Carleton Starkey, Indianapolis, Ind.,- assignor to Fletcher Trust Company, Indianapolis,

Ind., a corporation Application December 20, 1944, Serial No. 568,996

l This invention relates to a load limiting clutch wherein the torque load may be varied, and havz5 claims.I (ci. isz-56) ing many applications in respect to releasing a l driving connection -upon an overload being applied to a driven member, and particularly in association with a spring clutch acting as the torque limiting driving connection between the driving and driven members, reference being had to my pending application Serial No. 508,601, filed November l, 1943, entitled Torque limiting device now Patent Number 2,459,972.

The invention is particularly useful and applicable in not only maintaining a predetermined driving force, such as may-be controlled to a i certain number of foot pounds, but to selectively Avary such predetermined driving force through manual manipulation. I

For example, the invention may be applied to `the transmission of a machine such as aroad grader. or any of the power transmitting elements thereof, to permit slippage of the clutch to render ineffective the source of power in event of an obstruction or overload, and wherein by manual shifting, th.- predetermined `overload may be varied, depending upon the required work to be done and the capacity of the machine. For example, to eliminate unnecessary wear and tear upon the driving parts or elements of a road grader or bulldozer during normal service, the variable control may be set tola low degree of torque load, such as to effect slippage of the clutch in event such load is exceeded. However, there may be occasion to temporarily subject the machine to a much greater torque load to accom- ;plish a given purpose, such as the removal of a boulder or stump, whereupon the operator may shift or set the clutch to function up to a higher predetermined "load, after which it mayl bev returned to normal. It is further desirable that there bea vmaximum load carried by the clutch beyond which breakage might occur. and beyond 2 lessA degree of compression to vary its torque transmitting characteristic. d

A further feature of the invention resides in the provision of a reversible load limiting drive. wherein a reversing element may be actuated to varying positions for controlling the torque load on the driven element when driven in either forward or reverse direction.

Still a further feature of. this invention resides in the relation ofl the clutch spring or its respective coils to the clutching surface such that the clutching action will be initiated at the load carrying end of the spring and progress to the energizing end thereof. Similarly the declutching action will be caused to progress from the energizing end to the load carrying end. 'Ihis provision eliminates sudden grabbing of the clutch v such as to cause a chattering effect during the overload clutching and declutching action.

From the foregoing it will be observed that A the invention has many applications, particularly which the operator cannot increase the load carrying capacity, whereby upon the load exceeding a predetermined maximum, the clutch will slip and avoid breakage.

The invention, therefore, contemplates the application of a load limiting clutch as set forth and disclosed in -the above application, but

' wherein the clutch may be manually .set to drive at varying degrees oi' torque load within predetermined limits. This may be accomplished, for example, by providing an energizingA linger ory cam-like element engageable with the energizing end vof the clutch spring toy positively displace it relative to the load carrying end and to a more or wherein it is desirable to manually vary thel overload capacity and to shift from forward to reverse, and, therefore, among other things lis applicable not only to road graders and elements thereof, such as the scraping blade, butto bulldozers, trucks, hand and automatic tools, such as screw drivers, wrenches and the like. Thus, in

the former type of heavy duty machines, one yoverload capacity setting may be desirable for normal operation with a higher setting for special work, i. e., a short operation such as pulling a truck out of mud or up a bank. On the other hand, such light applications as in the latter `type, it may be desirable to apply the tool to a set of screws or studs Vunder one load application and re-set it for application to another set of screws or studs at a different load application. l The full nature of the invention will be understood from the accompanying drawings and the following description and claims.

Fig. 1 is a central vertical section through the driving mechanism with the clutch elements and driven shaft in elevation. Fig. 2 is a section taken on the line 2-2 of Fig. 1. Fig. 3 is a perspective view of the overload spring with a portion of the clutch spring connected therewith. Fig. 4 is the same as Fig. 1 with parts'broken away .and removed showing a modified form of clutch spring energizer and spring and pocket construction. Fig. 5 is the same as Fig. 1 with parts broken away and removed, showing a modified form of spring and pocket construction. Fig. 6 is the -same as Fig. 1 with parts broken away and reengagement between the energizing element and clutch spring. Fig. 'I is a section taken on the line 1-1 of Fig. 6. Fig. 8 is the same as Fig. 4 with parts broken away and removed, showing a modincation of the engagement between the energizing element and clutch spring.

In the form and operation of the clutch as in Figs. 1, 2 and 3, there is shown for purpose of illustration a transmission housing il mounting a driving member or shaft li and a driven member or shaft i2. It should be understood. however, that the driving force may be applied to the shaft i2 for driving the shaft il as the driven member. The shaft il extends into the housing, being rotatably supported by the bearing 13,;and terminating in a beveled pinion i4 adapted to mesh with and drive the beveled gears Ii and it in opposite directions. Thus, the gears l5, Il

and pinion Il constitute a reverse drive.

The gears i5 and i6 are provided with hubs I1 rotatable in the bearings I8 carried inthe housing, each of said hubs being formed with a clutch engaging drum here shown as a pocket provided with an internal clutch surface indicated at i9. As illustrated in Fig. 1, said clutch surfaces of the pockets are each tapered outwardly toward the open portion thereof, and are designed to each receive a clutch spring 2U which is generally cylindrical and so formed as to normally be supported out of clutching engagement with the internal clutch surface. Due to the taper of said surfaces, the inner or energizing ends of the'springs adjacent the open face of the pockets will be normally spaced a greater distance from the clutching surface than the opposite or load carrying ends.

. The shaft I2 extends through one of the pockets i1, with its thrust end extending into a recess in the opposite pocket to provide a supporting end bearing therefor, said shaft being normally rotatable within said pockets. The shaft l2 is pro vided with keyways 2l for receiving the down turned toe 22 on each of its overload release spring bands 23 to form a drivingkey between the shaft and the respective bands. Said bands are split at 24 and are normally of smaller diameter than the inner diameter of the pockets in which they are mounted to be adjacent the closed or reduced ends thereof. Thus, said bands are arranged to expand under a predetermined overv load, and upon such expansion permit slippage of their respective clutch springs in the manner hereinafter described.

Each of said bands has its inner face formed with a convolute surface to accommodate the end coil of the clutch spring 20, the free end of said spring abutting the shoulder 25 against which it is secured by a dowel pin 2S. The opposite end of the spring 20 is formed with a downwardly turned toe 21. The end of the springabutting and secured to the overload release spring 23 is herein termed the load carryinglend, whereas the opposite end of said spring provided with a toe 21 is termed the energizing end" thereof.

Slidably keyed upon the shaft I2 by the keys 2i!l and rotatable with said shaft there is a flanged shift collar 29. Said collar may be shifted along the shaft by avariable overload control or shift lever 20 engaging between the flanges of the l ,collar and pivoted to any suitable support at 3|.

The shift lever may be shiftable along a latching lbeu I2 and held in shifted position by a spring pressed ball- 33 operating in detents provided in said bar. Thus, the collar 29 may be manually shifted toward and away from the opposed springs 4 20 and may be set at any desired postion with respect thereto.

The shift collar 2l carries an opposed pair of spring energizing elements Il, each of which, as shown in Figs. 1, 2, 5, 6 and 7, may be in the form of a nger having a cam surface. These elements and the clutch springs 20 are so positioned relative to each other that upon the collar 29 being moved to a central position, said elements will not operably engage the springs. Upon the collar being shifted slightly to one side, the cam surface of one of the elements will engage the toe 21 of its adjacent spring and by reason of its cam formation will urge said clutch spring into its expanded clutching engagement within its pocket. Thus, as shown in Fig. 1, the right hand clutch spring has been engaged and expanded by the energizing element into clutching engagement with its pocket, whereas the left hand spring remains out of clutching engagement with its pocket to permit of free relative rotation therebetween.

At or about the point of overload release, it is desirable that the spring gradually clutch and declutch to avoid sudden action such as to produce chattering. For this purpose, there is provided a tapering relation between the outer clutching surface of the spring and the inner clutching surface of the pocket. The pocket of Fig. 1 is tapered so that the load carrying end of the spring lies closer to the friction surface than the energizing end of the spring. Therefore, upon the energizing element engaging the toe 21 and thereby expanding the spring, the load carrying portion of the spring will rst `expand into clutching engagement with the pocket. As the load is increased, said spring will gradually clutch the pocket progressively from the load carrying end toward the energizing end. This permits of a more gradual clutching and declutching action than would result if all of the coils of the spring were expanded simultaneously into clutching engagement throughout its entire length. Through this arrangement of the progressive clutching action from' the load carrying to the energizing end of the spring, chattering of the spring is avoided, i. e., intermittent grabbing and releasing. Also the clutching action thereof is more sensitive to the overload torque. This tapering relation between the spring and the pocket with the progressive clutching and declutching of the spring from one end to the other-also is important in facilitating action ofl the spring in permitting the maximum driving or overload torque to be varied in the following manner.

It may be here pointed out, for example, that 'when the shaft Il is the driving member and the shaft I2 the driven member, the hubs I1, and, therefore, the pockets, are normally driven in reverse directions in over running relation to the springs. Upon the energizing element 24 being moved into engagement with the toe 21 of one of the springs to expand it. such expansion rst causes the opposed load carrying end of the engaged spring to clutch the pocketadjacent the band 23. The clutch spring will thereu'pon rotate in the direction of the arrows with the pocket, its load carrying end being in abutment with the shoulder 25 of the spring band 23 to thereby rotate said band. The band in turn, being keyed to the shaft I2. will correspondingly rotate said shaft. However, upon said shaft being overloaded beyond a predetermined foot pound, the resistance to further turning of the shaft lis traninnitiedv to the band through the key 22, causing the band to be expanded by thedriving force ofthe spring. Upon the band being thus expanded, it permits of relative -rotation between the load end portions of the spring at 2l and the stillexpanded and therefore clutch-active coils of the spring soy as to render the clutch spring partially inactive by contracting the load carrying end portions of the spring away from the pocket while leaving energizing end portions of .thecoils sun'iciently engaged with the pocket to carry the normal torque. Upon the overload being lessened, the band 22 will return to its normal position, pulling the load end of the spring at 2B in the reverse or expanding direction back to full clutching )engagement with the pocket. i

'I'he spring band may be so formed and constructed as to expand to release the clutch at a predetermined foot pound, for example,twenty foot pounds. Thuswith the normal engagement of the spring by the energizing element, as shown cylindrical clutch pocket il in Fig. 1, the shaft will be driven under a torque load up to twenty foot pounds. Upon the load being inexcess thereof. the band will give or expand to eil'ect declutching through the slippage of the clutch spring. However, the overload may be increased by varying the position of the energizing end of the clutch spring at the toe 21. Since the declutchingor slippage of the spring is dependent upon the relation of the opposed ends thereof at and 21, by changing that relation the load at which the spring will declutch or slip through the action of the band 23 may be increased. The energizing element 3 is, therefore, designed with a camming surface so that as it is moved inwardly toward the spring, its camming surface in engagement with the toe 21 will displace it toward the load end of the spring at 25. The clutch spring is, therefore, not only under greater compression, but'a correspondingly greater movement of the load carrying end will be required to release it. Such further movement of the loadcarrying end is occasioned only by a greater expansion of the band 23 under a heavier torque load.

In view of the above, by means of the lever 3l', the energizing element may be moved to different positions relative to the toe of the spring, andl by reason of its camming surface will vary the relation thereof in respect vto the load end of the spring at 25, such as to increase the load necessary to cause suiicient expansion of the band 23 and corresponding movement of the load carrying end of the spring, such as to permit its contraction out of full clutching engagement. Such camming' action, however, is limited'in extent -by the limitfpins 35 secured on the shaft i2 and sopositioned as to be engaged by the sliding collar 29. Said pins may thus be suitably' positioned relative to the collar 29 and thecamming surface of the energizing elements 34 to limit the yextent to which the load may be increased, and thereby provide for a maximum load capacity.

In the modified lform of Fig. 4, the hubs of the gears l5 and IS-'are provided with a straight cylindrical pocket H1, as distinguished from the tapered pocket l1 of Fig. 1. To permit of the progressive clutching-action of the clutch spring in the straight cylindrica1 pocket, said spring is provided, with a series of grooves indicated by the dotted lines at I2l, andy wherein the depth at which said grooves are cut progressively increases from the energizing end at the toe 21 K4 to'the'load carryingend indicated at 2l..-

' compasses a tapered clutch spring In this Vconstruction of clutch spring there will be less/resistance to expansion into clutching engagement where the grooves ill are of greater depth. This permits of the expanding action of the spring being transmitted first to the-load .carrying end where the grooves i2l'are of the greatest depth, since such portion'of the spring will be the more flexible. a

Also, as shown in the modified form of Fig. 4, the energizing element is in the form of a spring linger |84, the spring resilience of the finger having the same enect upon the energizlng toe 21 of the spring as the camming surface of the energizing element Il.' Thus, as the collar 2l is moved toward the clutch spring, the spring finger Il! will, under its inherentspring tension, exert a greater expanding forceon the clutch spring to thereby increase the point of overload release accordingl In the modified form of Fig. 5, the straight 1, as in Fig. 4, en-

220, the clutch y greater thickness at its energizing end than at its load carrying end. Thus, the coils ofthe spring at the load carrying end are slightly weaker and, therefore, more susspring being of ceptible of expansion into clutching engagement than at the energizing end. By means of such tapered spring, upon the spring being energized for expansion into clutching engagement with the pocket, such action will be transmitted throughout the series of coils, causing the weaker coii'at the load carrying end to rst expand into clutching engagement followed progressively from that end toward the energizing end of the spring in accordance with their respective cross sectional areas. l

In the modined form of Figsf and 7, the clutch spring 220 is formed with the'energizing toe 321 extending laterally toward the energizing element 24 for engagement thereby. Thus, instead of the toe extending radially inwardly, as in Figs. 1 and 2, with the energizing element engaging therewith and movable .within the coils of the spring, by means of the arrangement shown in Figs. 6 and 7, the energizing 'element may move in the plane tangential to' the spring and produce its variable overload release action through its sliding engagement with the elongated laterally directed toe321. A similar arrangement is shown in the modified form of Fig. 8 wherein the laterally-extending elongated toe 321 of the clutch vspring 320 is engaged by the energizing element in the form of a spring finger Ill. 4 Whereas the invention has been above decribed in respect to one adaptation thereof with various modifications, the variable load limiting clutch is similarly applicable to various'drivlng mechanisms, as well as tools and devices for applying a limited torque load, and wherein it is desirable to vary the minimum torque load at which the device will release up to a maximum overload.

Also. as illustrated herein,the clutch is aps plicable to a reverse drivingfmechanism and wherein the variable control of the overload release also acts as lthe reverse drive control mech- When the lever is moved in the opposite direcanism. By means control lever 30 being moved in one direction to varying degrees, thev load will be variably limited in a given direction to the extent of' the variable movement in that direction of the lever.

of this arrangement`upon theV said members tending to relieve tion the power will be applied in the opposite direction to an extent in accordance with the movement in that direction of the lever. When the lever-is in intermediate or neutral position,

` the driving power will be disconnected and there transmission of the overload while at the same time maintaining the desired driving torque.

The invention claimed is:

1. A variable load limiting clutch including a driving member, a drivenmember, one of said members being provided with a clutch engaging surface, a clutch spring having a series of expansible and contractible coils mounted for movement into and out of effective driving engagement with said clutch engaging surface, load sensitive means interconnecting said clutch spring and .the tive upon an overload being applied to one of at least part of said clutchl spring from clutching engagement with said clutch engaging surface thereby lto render partially ineffective the driving connection between said members, and a shiftable element engageable with one end of said clutch spring for affecting its relation to said load sensitive means in a manner to vary the overload required to render said driving connection partially ineffective.

2. A variable load limiting clutch including a driving member, a driven member, one of said members being provided with a clutch engaging surface, a clutch spring having a series of expansible and contractible coils mounted for movement into and out of clutching engagement with said clutch engaging surface to provide a driving connection between said members, a load sensitive spring operable under a predetermined torque force exerted thereon by an overload applied to one of said members to permit relative movement between one of said members and said load sensitive spring, said relative movement being leffective to permit said clutch engaging spring to move in a direction out of effective clutch engagement with said clutch engaging surface and a control element operable so to move said clutch spring as to vary the overload required.

3. A. variable load limiting. clutch including a driving member, a driven member, one of said Y members being. provided with a. clutch engaging surface, a clutch spring having a series of expansible and contractible coils movable into and out of effective clutching engagement with said surface, a load sensitive spring interconnecting said clutch spring and the other of said members effective upon an overload being applied thereto to permit said clutch spring to Amove in a direction out of clutching engagement with said surface, and an energizing element engageable with one end of said 'clutch spring, said element being shiftable to move said clutch spring variably to different operative positions whereby to vary the overload required to permit said clutch spring to move in a direction away from said clutch engaging surface.

4. A variable load limiting clutch including a.

other of said members and eifecmembers being provided with a clutch engaging surface, a clutch spring having a series of expansible and contractible coils movable into and out of engagement with the clutch engaging surface of said last-mentioned member, a load sensitive spring interconnecting said clutch spring and the other of said members and eifective upon an overload being applied thereto to permit said clutch spring to move in a direction out of clutching engagement with said clutch engaging surface, and an energizing element engageable with one end of said clutch spring and shiftable to displace said end relative to the opposite end thereof to increase the clutching force of the spring and thereby increase the lwrque load required to permit said opposite end of said clutch spring to move out of effective clutching engagement with said clutch engaging surface.

5. A variable load limiting clutch including a driving member, a driven member, one of said members being provided with a clutch engaging surface, a clutch spring having a series of expansible and contractible coils movable into and out of clutching engagement with said surface, a load sensitive spring having one end operatively connected with the load carrying end of said clutch spring and the other end thereof connected with the other of said members and eifective upon an overload being applied to one of said members to effect the displacement of the load carrying end of said clutch spring away from the clutch engaging surface thereby to render the clutch engaging surface at least partially ineffective asadriving connection between said members. and an energizing element engageable with the energizing end of said clutch spring and shiftable to displace said energizing end relative to said load carrying end to increase the clutching force thereof and thereby increase the overload required to render said clutching engagement partially ineffective.

6. A load limiting clutch, including a driving member, a driven member, one of said members being provided with a drum having a clutch engaging surface, a clutch spring having a series of expansible and contractible coils movable into and out of clutching engagement with said drum, said clutch spring being normally out of engagement therewith and having a load carrying end vand an energizing end, said clutch spring being movable into clutching engagement with said drum upon said energizing end being displaced in one direction relative to said load carrying end, and a load sensitive spring interconnecting the load carrying end of said springend the other of said members to effect a driving connection between'said members upon said clutch spring being expanded into clutching engagement with said clutch engaging surface, said load sensitive spring in response .to an overload applied to Ione of said members being adapted toeil'ect relative movement between theload carrying end and the energizing end of said clutch spring. whereby said spring will tend to move out of eifective clutching engagement with said clutch engaging surface. 'LA load limiting clutch including a driving member, a driven member, one of said members being provided with a drum having a. clutch ,en-

gaging surface, a clutch spring having aseries of expansible and contractible coils movable into and out of clutching engagement with said drum and normally' out of clutching engagement therewith, said clutch spring having an energizing end and a load carrying end, a load sensitive spring driving member, a driven member, one of said interconnecting the load carrying end of said ioad carrying end and .annoso force, to urge said clutch` spring in a directionout of clutching engagement with said clutch engaging surface.

, 8. -A load limiting'v clutch, including a'driving member, a driven member. one of said members being provided with a drum having a clutch engaging surface, a clutch spring having a. series .of expansible and contractible coils movable iniziand out oi'v effective driving clutching engage- Yment with the drum of said last-mentioned member, said clutch spring being normally out of Atherewith and having a an energizing end, said clutch spring being expamible into clutching engagement lwith said drum upon said energizing end being displaced Vrelative to said load carrying end, an energizing element on the other of said members operating to displace said energizing clutching engagement end and a load sensitive spring `interconnecting the loa'd carrying end of said clutch spring and the other of said members to eil'ect'a driving connection between said members iupon said clutch spring being expanded into clutching eniof j clutch engaging surface.,said-clutchl spring havspring through l displacement said drum having one end secured to said driven member and the other end thereof operably connected with the load carrying end ofl said. clutch which saidclutch spring when in clutching engagement with said drum is adapted to directly drive saidv driven member. said band being expandible upon a predetermined overload being applied to said driven member to eifect of the load carrying end of said clutch spring relative to the energizing end thereof to thereby tend to move the spring out of clutching engagement with the clutch engaging surface of said drum.

11. A variable load limiting clutch, including" a driving member having a spring olutch'engag- 'mally out of clutching ing drum, `a driven member tive to said driving member, said drum having a clutch engaging surface. va clutch spring having a series of expandible and contractible coils norengagement therewith, said clutch spring havingan energizing end and a load carrying end, a split springfband having e one end secured to said driven member and the gagement, said load sensitive spring being affected V by, 'an overload applied to one of said members ,to permit of relative movement between the load carrying end and the ,energizing end of said clutch spring whereby saidjclutch spring will tend to move out of clutching engagement, said energizing element being shii'table to displace the energizing end of the lclutch spring relative to the load carrying end thereof to thereby increase the overload required to permit slippage of the lclutch spring.

9. A variable load limiting clutch including a'A driving member having a spring clutch receiving drum, a driven member freely rotatable relative to said driving member, said drum having a clutch engaging surface, a clutch spring having and contractible coils nora series of expansible mally out of clutching engagement with said drum and expandible into clutching engagement therewith, said clutch spring having an energizing end and a load. carrying end, a load sensitive spring vmounted about said drum and having one end secured to said driven member and the other end opera-bly connected with the load carrying end of said clutch spring, and a shiftable enersizing element onerablv engageable with the energizing end of said clutch Spring to'move it into clutching engagement with said drum for transmit-ting power therefrom through said load sensitive spring. said load sensitive gni-ing being expandible upon an overload being -armlied to said driven member for permitting relative movement between the load carrying end of'said clutch spring and the energizing end thereof to permit movement of said clutch spring in a direction out of clutching engagement with said drum.

10. A load limiting clutch, including a driving member having a spring clutch engaging drum. a driven member freely rotatable relative to said driving member, said drum having a clutch engaging surface, a clutch spring having a series of expandible and contractible coils normally out oi' clutching engagement withsaid drum and exto the driven membery tractible coils normally out of Aapplied to said driven member gizingl end thereof in a direction other end thereoifoperably connected with the which said clutch spring when in clutching engagement with said drum is adapted to directly drive said driven member, said band being expandible upon a predetermined overload being to effect displacement of the load carrying end of said clutch spring relative to the energizingend thereof in a direction tending to move said clutch spring out of clutching engagement with said pocket, and an energizing element shiftable to varying positions relative'to the energizing end of said clutch spring to vary its relative position in respect to the load carrying'end thereof to thereby increase the displacement of the load carrying end and said split band required partially to declutch said clutch 'spring through the application of a load greater than said predetermined l overload.' f I 12. A variable load limiting clutch, including a driving member having a. spring clutch engaging drum, a driven member freely rotatable relative to said driving member, said drum having an internal clutch engaging surface, a clutch spring having a series of expandible and conclutching engagement with said drum and expandible into clutching engagement therewith, said clutch spring having an energizing end and a load carrying end, a split spring band having one end secured to said driven member and the other end thereof operably connected with Ithe load carrying end of said clutch spring through which said clutch spring when in clutching engagement with said drum is adapted to directly drive said driven member, saidv band being expandible upon a predetermined overload being applied to said driven lmember to eect displacement of the load carrying end of said clutch spring relative to the enersaid clutch spring out of clutching engagement with said drum,an energizing element shiftable .to varying positions relative to the energizing end of said clutch spring to vary its relative position in respect to the load carrying end Vthereof to thereby increase the displacement of the load carrying end and said split band requiredto partially declutch saidclutch spring through the appandible into clutching engagement with said `p1ication of a load greater than saidpre'determounted concentric with l Y freely rotatable relatending to movemined overload, and means for limiting the movement of said element and displacement of the energizing end of said clutch spring thereby to limit the increase in overload at which said clutch spring will move toward declutching position.

13. A spring clutch device including a driving member, a driven member, one of said members being provided with a surface having a clutch engaging surface, a clutch spring having a series of expandible and contractible coils movable into and out of clutching engagement therewith, means for connecting the load carrying end oi' said clutch spring with the member other than that provided with said surface, said clutch spring being normally out of clutching engagement with said drum and axially movable means engageable with the energizing end of said clutch spring to effect the expansion thereof into clutching engagement with said surface, said clutch spring and pocket being so tapered relative to each other that in their normal position out of clutching engagement each coil will be spaced 'a greater distance from said surface progressively from the load carrying end to the energizing end of the clutch spring, whereby upon said clutch spring being' energized the expansion thereof will tend to eifect clutching engagement with said surface progressively from the load carrying end to the energizing end of said clutch spring.

14. A spring clutch device including a driving member, a driven member, one of said members being provided with a drum having a clutch engaging surface, a clutch spring having a series of expandible and contractible coils movable into and out of clutching engagement therewith and normally out of clutching engagement, means for connecting the load carrying end of said spring with the member other than that provided with said drum, and meansv for operatively engaging the energizing end of said spring to eiect movement thereof into clutch engagement with said drum, the coils of said spring being progressively weakened from the energizing end toward the load carrying end, whereby upon being energized to expanded position at the energizing end the weaker coils at the load carrying end will be caused to rst expand into clutching engagement with said drum and be the first to be released from said clutching engagement upon said spring moving to declutching position.`

15. A load limiting clutch including a driving member, a driven member, one of said members being provided with a clutch engaging surface, a clutch spring having a series of expandible and contractible coils movable into and out of clutching engagement with said clutch surface, means associated with one of said members for operably engaging the energizing end of said clutch spring to urge its expansion into clutching engagement with said clutch engaging surface, and a load sensitive spring connecting the opposite load carrying end of said clutch spring to the other of said members, whereby upon a predetermined overload being applied to said load sensitive spring it will permit relative movement between the ends of said clutch spring tending to relieve said coils from their clutching engagement with said clutch engaging surface, said clutch spring being so related to said clutch engaging surface that the coils of the former will tend to move into or out of clutching engagement with the latter progressively from the end of the clutch spring connected with said load sensitive spring to the other end ofI said clutch snrlns. A

16. A variable load limiting clutch including a driving member, a driven member, a clutch mounted for engagement with one of said members, load sensitive means interconnectingl said clutch and the other of said members and effective upon a predeterminable overload being applied to one of said members to effect at least partial slippage of said clutch relative to said first-mentioned member, and a control element operatively engageable with said clutch to change its relation with respect to the load sensitive means to thereby vary said overload point necessary to permit slippage of said clutch.

17. A variable load limiting clutch including a driving member, a driven member, a clutch element mounted for clutching engagement with one of said members to provide a driving connection with the other of said members, a load sensitive element operable on the clutch element under a torque force exerted thereon by an overload applied to one of said members to permit slippage of said clutch element upon relative movement between said members and a control member operable on one of said members to vary the over load value necessary to enable such relative movement.

18. A variable load limiting clutch lncludin! a driving member, a driven member, a spring coil type clutch for connecting said members, a load sensitive element interconnecting said spring clutch and one of said members and effective upon an overload being applied thereto partially to declutch said members, and an energizing element engageable with said clutch and operable to move said spring clutch to varying positions affecting its relation to said load sensitive element to thereby vary the partial declutching overload.

19. A spring clutch device including a driving member, a driven member, one of said members being provided with a clutch engaging surface. a clutch spring having a series of expansible and contractible coils movable into and out of clutching engagement with said clutch engaging surface and normally out of clutching engagement therewith, said spring having an energizing end and a load carrying end, means for connecting the load carrying end of said spring with one of said members, means associated with the other of said members for operably engaging the energizing end of said spring to eect relative movement between the energizing and load carrying ends thereof to move it into clutching engagement with said clutch engaging surface, said spring and clutch engaging surface being so related as between the energizing and load carrying ends of said spring to transmit its energizing action first to the coils thereof at the load carrying end to effect clutching engagement thereby. said clutching engagement of the load carrying coils acting progressively to move the coils into clutching engagement with said surface from said load carrying end to the energizing end of the spring.

20. A spring clutch device including a driving member, a driven member, one of said members being provided with a clutch engaging surface, a clutch spring formed with progressively weaker coils from its energizing to its load carrying end, said coils being normally out of clutching engagement with said clutch engaging surface and movable into clutchingengagement therewith. means for connecting the weaker coils of the load carrying end of said spring' Vwith the member that provided the clutch m linto clutching engagement with said surface whereby said energizing action will be transmitted from the energizing end of said spring to first move the weaker coils at the load carrying ,end thereof into clutching engagement and said load carrying coils will cause the coils of said spring to be progressively moved into clutching engagement with said surface toward the energizing end of said spring.

21. A spring clutch device including a driving member, a driven member, one ofsaid members being provided with a clutch engaging surface, a clutch spring having a series of expansible and contractible coils mounted for engagement with said clutch surface and movable into and out of clutching engagement therewith, means for connecting the load carrying end of said spring with the member other than that provided with a clutch engaging surface, said spring being normally out of clutching engagement with said surface, and means for operably engaging the energizing end of said spring to eiect expansion thereof into clutching engagement with said surface, said spring and clutch engaging surface being so tapered relative to each other that in their normal relative positions out of clutching engagement each coil will be spaced a greater distance from said surface progressively from the load carrying end to the energizing end of vsaid spring,

whereby upon said spring being energized the load carrying end thereof will first clutch said clutch surface followed progressively by clutching of the coils therewith from the load carrying end to the energizing end of said spring.

22. A spring clutch device including a driving member, a driven member, one ofsaid members being provided with a drum having a clutch en gaging surface, a clutch spring mounted for clutching engagement withsaid pocket normally out of clutching engagement therewith, means for connecting the load carrying end of said spring with the memberother than that providedv with said drum, and axially movable means engageable with the energizing end of said spring to urge the spring into clutching engagement with said drum,'diiere'nt portions of said clutch spring and associated portions of said drum being so related vin .respect to tendency toward clutching engagement that the expansion of said clutch spring from the energizing end thereof Awill effect clutching engagement first at the load carrying lend of said clutch spring and progressively therefrom Itoward the energizing end thereof. v

23. -A variable load limiting clutch including a driving` member, a driven member, one of said members having a clutch surface, a helical clutch spring mounted 'for clutching engagement with said clutch surface, a`load sensitive spring elementl interposed'between' one end of said clutch spring and the other of said members to transmit torque. therebetween and effective upon overload to permit slippage of said clutch spring, and a control element carried by and rotatable with the said other member operably engageable with the opposite. en'd of said clutch spring'adjustable to different positions relative thereto for varying the Y angular relation of the ends of said clutchv spring to thereby vary the overload torque under which said load sensitive-spring will permit slipplse of said clutch sll'illl.-v

Number Name Date 801,727 Lindsay et al.. Oct. 10, 1905 852,045 Vivinus 'Apr. 30, 1907 998,615 Huneke July 25, 1911 1,561,537 Hayes Nov. 17, 1925 1,615,804 Starkey Jan. 25, 1927 1,629,098 Drexler '..--gvs May 17, 1927 1,704,062 Starkey Mar. 5, 1929 v1,819,306 Starkey et al. .Aug. 18, 1931 1,836,199 Starkey Dec. 15, 1931 `1,870,646 Pitter Aug.v 9, 1932- 1,953,370 Starkey .L g Apr. 3, 1934 2,024,947 Racklyeft Dec. 17, 1 935 2,043,695 Brownlee June v9, 1936 2,229,654. 'Hubbel1 .s Jan. 28,

2,235,266 f Starkey 'Mar. 18, 1941 2,360,187 Almen i.- Oct. 10, 1944 24. A 10aa limiting' clutch including a drivingv gagement with the energizing end of said clutch' spring to permit said spring to declutch said surface upon said element being axially moved from engagement therewith and urge said spring into said clutching engagement upon being moved to energizing engagement therewith, and a load sensitve spring interposedbetween the load carrying end of saidclutch spring and the said other member to transmit torque therebetween and yield under overload to permit relative movement between the energizing and vload carrying ends of said clutch spring in a direction tending to relieve said coils from their clutching engagement with said clutch engaging surface.

25. A torque transmitting device comprising a friction drum, a coaxial torque element, a helically coiled elastic friction band between the drum land element and normally out of contact with of`- operation of the device whereby initial contact between the band and drum is at the highest pressure producing region of the band under all loads yet the band cannot become self-energizing and thereby take control of the maximum clutching pressure away from the energizingy control connection.

WILLIAM CARLETON STARKEY.

REFERENCES CITED The following referencesfare of record inthe ille of this patent:

UNrrED sTATTzs PATENTS 2,371,855 Sunderland-aun Mar. 20, 1915 

